The transducer art is replete with devices wherein a magnetic or ferromagnetic shunt or armature is moved in the magnetic circuit of one or more electromagnetic coils so that readout equipment responsive to the inductance change can be activated to relate the movement of the armature or shunt to a desired measurand. Typical of such devices are "E" core inductive transducers and displacement sensors that exploit the changes in the self (or mutual) induction by moving a permanent magnet relative to a high-mu core of a solenoid. The idea of measuring external magnetic fields by observing changes in the reactance of a toroidal coil caused by variations of the effective permeability due to the field under observation has also been suggested (Instrumentation in Scientific Research Lion, Kurt S., 1959, pp 199-202) but the system described therein is stated to have nonlinear characteristics and requires empirical calibration.
Pressure measurements are frequency used for medical diagnosis and treatment and in scientific and industrial situations. Examples of typical uses for the invention would be monitoring physiological pressure, industrial processes, scientific studies such as siesmic waves, etc.
Prior art transducers useful for measurement of pressures have certain inherent limitations. Many prior art transducers such as the Wheatstone bridge, quartz crystal and piezoelectric are sensitive to sudden fluctuations in temperature. Operation of prior art transducers require careful control of the environmental temperatures and the temperature of the mediums being measured. If the temperature effecting the device should vary by as little as ten degrees Fahrenheit. then the accuracy of the measurement is affected. Several devices of the Wheatstone bridge type must go through a delay in use while internal electrical means are used to achieve operating temperature stability. Should sufficient temperature variations occur during use it then becomes necessary to recalibrate the device, introducing undesirable delays in procedures.
Several prior art devices may be damaged or may need recalibration if they are subjected to mechanical shock. Normal use of these devices does require unusual care to protect the device from relatively minor levels of physical shock, such as produced when the device is dropped.
Certain prior art devices lack sufficient sensitivity for many of the technical demands of the medical, scientific, and industrial professions. Certain devices will not sense small changes in applied pressures that occur in short periods of time. Many prior art devices lack the sensitivity to respond to small pressure changes.
Several prior art devices have certain inherent delays in their response to pressure changes. Design limitations delay the initial response by a device to an applied pressure. Design limitations can delay the time for the device to return to a resting state after an applied force has been removed. Such fluctuations in response characteristics introduce potential sources of error for time related analysis of pressure variations.
Certain prior art devices are subject to damage or the need for recalibration if they are exposed to applied pressures outside of relatively narrow operation limits. A device can be overpressurized by process failures and errors in user technique during installation and use. Delay in data collection and possible collection of incorrect data can be caused by overpressurization and damage to prior art devices.
A small excitation current is generally necessary for proper function of prior art devices with the physical constraints of designs of prior art devices resulting in devices that use a fragile pressure sensing diaphragm to electrically insulate the transducer excitation from the fluid being observed. Pressure responsive diaphragms are subject to rupture, allowing fluids or gases to come in contact with the electrical portion of the transducer producing a finite and potentially hazardous current leakage.